Current commercial aircraft designs are drawn to eliminating the need for having three operable high-grade (i.e., navigation grade) air-data inertial measurement units for obtaining aircraft attitude measurements. The desire is to have an aircraft that includes only two high-grade inertial measurement units, and have a third unit that may be a low-grade inertial sensor, such as a micro-electromechanical (MEMS) inertial sensor. At the same time, there is a desire to maintain the capability for the aircraft to take-off, even when one of the two high-grade inertial measurement units is out-of-service (for example, due to an inertial sensor fault). Take-off and operation of an aircraft with two reliable sources for attitude measurements is not problematic in itself, but a situation can develop where one of the two remaining in-service inertial sensors degrades during flight and begins to output attitude data that includes some level of bias error. In that case, when the flight crew observes that the two in-service inertial sensors are producing differing roll and/or pitch data, they need to be able to determine which of the sensors is providing accurate attitude measurements and which is not.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for alternate systems and methods for attitude fault detection based on integrated GNSS/inertial hybrid filter residuals.